1. Field of the Invention
The present invention relates to a headlight for an automobile and more particularly to a headlight utilizing a single movable light source capable of changing its light distribution pattern to conform with any illumination guidelines governing the situations wherein the automobile is traveling straight ahead or by-passing another vehicle. This invention can also be employed to dim the headlights from its highbeam operation to accommodate the approach of on-coming vehicles. A headlight according to the present invention is particularly suited for those headlights utilizing a metal halide lamp, which because of their construction cannot be positioned close together and, therefore, are unable to comply with the above described situations separately.
2. Discussion of the Related Art
Japanese Patent Application HEI 08-111101 discloses a conventional headlight. The light source is coupled to and is supported by a rotatable vertical lever. When an automobile by-passing another vehicle, a lever rotates backward by a predetermined angle around the rotary axis on the upper part of the lever and the light source is moved concurrently backward and downward.
However, as depicted in FIG. 6, when the automobile with the above described headlight is traveling straight ahead, the optical axis X of the light source 90 tilts downward by degree alpha relative to the optical axis Z of the reflector 91. Accordingly, the arc 90a of the light emitted from the light source 90 also tilts and modifies the light distribution pattern that gives rise to the following problems. Firstly, it is difficult to have a light distribution pattern sufficient for both situations, when the automobile is traveling straight ahead and when the automobile is by-passing another vehicle. Secondly, it is difficult to satisfy any potential headlight operational guidelines, when a metal halide lamp is used as a light source, because the optical axis X of the light source 90 when the automobile is traveling straight ahead has to be positioned so that the light source 90 is tilted 10 degrees or less from the optical axis of the reflector. If the optical axis X tilts more than 10 degrees, it is prone to shorten the life of the automobile headlight. Additionally, an automobile headlight having a metal halide lamp as a light source is required to have means for adjusting excessive brightness in the forward and upward directions, when the automobile is carrying a heavy load, and this is accomplished by tilting the optical axis X of the light source 90 upward. Thirdly, the use of the rotatable lever substantially increases the size of the headlight, because the lever has to be long enough to satisfy any operational guidelines such as, a requirement that the optical axis X of the light source 90 is required to move backward from 3 to 5 millimeters and downward from 0.5 to 1.5 millimeters.